1. Field of the Invention
The present invention relates to a method of producing ventilator grills for use in ventilation systems such as automotive air conditioners. More particularly, the invention is concerned with a method of producing a ventilator grill of the type which comprises a grill frame and substantially parallel louver vanes pivotally mounted on the grill frame, the grill frame including a pair of opposite sides in which aligned pairs of axle holes are formed, the louver vanes having axles extending from the opposite ends of the vanes respectively and rotatably received in respective aligned pairs of axle holes, the grill frame being provided with at least two recesses formed in the outer surfaces of the pair of opposite sides of the frame and communicated with one of the aligned pairs of axle holes, the louver vane associated with the one aligned pair of axle holes having disc-like friction portions integrally connected to the outer ends of the axles of the one vane and received in the recesses rotatably but frictionally to provide a slight frictional resistance to angular movements of the louver vane relative to the grill frame.
2. Description of the Prior Art
The specification of Japanese Pat. No. 990,864 (Post-Examination Patent Publication No. 54-26,266 published Sept. 3, 1979) discloses a method of producing a ventilator grill of the class specified above. According to the method disclosed in the Japanese patent specification referred to above, a prefabricated grill frame of a first plastics material is inserted into a louver forming mould. Then, a second plastics material having a melting point different from that of the first plastics material is injected into the louver forming mould to form a louver. The prefabricated grill frame is provided with axle holes formed in the two opposite sides of the grill frame. Circular recesses are formed in the outer surfaces of these opposite sides of the grill frame and communicated with the axle holes. Thus, the second plastics material injected into the louver forming mould fills up the louver vane moulding spaces and also the axle holes and recesses in the prefabricated grill frame to form louver vanes having axles extending from the opposite ends of the vanes and circular friction portions integral with the outer ends of the axles. When the second plastics material is cooled and solidified, the material slightly shrinks radially inwardly within the axle holes so that the second plastics material solidified in the axle holes is slightly spaced from the inner surface of the axle holes to allow louver vanes to be rotated relative to the grill frame. The shrinkage also takes place in the axial direction of the axle holes to slightly inwardly bias the disc-like friction portions against the bottoms of the recesses. The friction portions, therefore, cooperate with the grill frame to produce a slight frictional resistance to the angular movement or rotation of the louver vanes relative to the grill frame.
The ventilator grill producing method disclosed in the above-mentioned Japanese patent publication eliminates conventionally required complicated steps of fabricating the grill frame and the louver vanes separately and then assemblying the grill frame and the louver vanes so that the vanes are rotatable with respect to the frame. Thus, the prior art method not only greatly improves the productivity but also assures the production of ventilator grills which are operative to reliably control the direction of the flow of air through the grill because the friction between the disc-like friction portions of the vanes and the grill frame is sufficient to hold the vanes at any desired angular orientation. However, the prior art method discussed above inevitably includes the step of inserting a prefabricated grill frame into a louver forming mould and thus falls short of satisfying the demand for an improved continuous production of individual ventilator grills.
Japanese Pre-Examination Patent Publication No. 53-19372 published Feb. 22, 1978 discloses another method of producing a ventilator similar in type to the ventilator grills manufactured by the method disclosed in the Japanese patent specification referred to above. In the other ventilator producing method, one mould is used which defines therein cavities for moulding a grill frame and for moulding louver vanes. A first plastics material is injected by a first injection cylinder into a first or grill frame moulding cavity to form a grill frame having axle holes and coaxial recesses formed therein. For this purpose, the mould is provided with a plurality of sets of complicated plungers each comprising a pair of telescopic plungers one of which is an outer tubular or sleeve-like plunger and the other of which is a rod-like plunger slidably received in the outer sleeve-like plunger for relative axial movement. When the first plastics material is injected into the grill frame moulding cavity, the outer and inner plungers are extended into the grill frame moulding cavity to their innermost or most extended position in which the inner rod-like plunger projects a distance from the outer sleeve-like plunger so that the inner and outer plungers act as cores for moulding the axle holes and coaxial recesses in the grill frame thus moulded. After the first plastics material has been solidified in the cavity, the inner and outer plungers are retracted to their outermost or most-retracted position in which the end faces of the inner and outer plungers are flush with each other and also with the outer surfaces of the sides of the grill frame in which the axle holes and recesses have been formed. Then, a second plastics material having a melting point lower than that of the first plastics material is injected by a second injection cylinder into the louver vane moulding cavity and into the axle holes and recesses formed in the grill frame.
The second method needs a complicated mould because two plastic inlet ports for connection with two injection nozzles for the first and second plastics materials must be formed in one mould. In addition, the method calls for the use of a plurality of sets of complicated cylinders each comprising a pair of telescopic outer or sleeve-like plunger and an inner rod-like plunger for moulding the axle holes and the coaxial recesses in the grill frame.